Refrigerator Designs of the 1930s and 40s
In the 1930s, refrigerator sales were booming. New manufacturers were coming on the scene every year. It was an experimental bonanza, with no holds barred on innovations.
There was the top-mounted “drop-in” unit for easy repairs and replacement, with every conceivable type of compressor. Two mail-order catalog houses featured top-mounted drop-in units that had direct-drive compressors with two horizontally opposed cylinders. Also included in this format was the belt-driven rotary compressor, single- and twin-cylinder compressors, and the original “Monitor Top” sealed unit.
The first unit to use a capillary tube (made of brass tubing) was also top mounted. Quite a few contractors specialized in remote basement installations for homes that had large, custom-made refrigerators in their kitchens.
Ehrens AwardsIt would be sinful to reminisce and fail to give “Ehrens awards” to some of the very radical sealed units used in early refrigerators.
Honorable mention should go to a refrigerator that used Carrene (methylene chloride) as a refrigerant, which operated with both high and low sides in a vacuum. In essence, it was the closest to our modern water chiller unit.
It had a cast iron, flooded-type evaporator with a high-side float as a refrigerant control. The only way of knowing there was a “leak” in the system was when air entered the unit and the high-side float became air bound, preventing refrigerant from entering the evaporator.
This was one of the most heavily advertised refrigerators; ads stressed the fact that it used the “safest cooling liquid.” After a few years, it disappeared from the market because of difficulty in servicing.
Third prize goes to the “Meter Miser,” a rotary compressor specifically designed for a newly patented refrigerant, Freon-114. The unit operated at about 12 in. of vacuum on the low side, had a rear static condenser, and a ¼ 20-hp motor. Even though it ran continuously on hot days, the total wattage by the month was less than half of the belt-driven units.
It had a very novel refrigerant control. Picture a headless bolt, 1-in. dia, 2-in. long, screwed into a brass tube, with a refrigerant inlet on one end and an outlet on the opposite end. This was another version of a capillary tube, where the refrigerant flowed around the threads of the bolt for the necessary pressure drop.
The entire unit was so economically designed that all defective units returned to the factory were scrapped and replaced with a new one.
Second prize should go to the improved Monitor Top. This was a large, top-mounted, round-shaped unit that was almost as wide as the 6-cu-ft cabinet. It had a wraparound, embossed plate-type condenser, a high-side float, and a flooded, plate-type, plated copper evaporator using methyl formate as the refrigerant. The rotary-type compressor was rather large, as it had to pump a considerable volume of vapor; methyl formate pressures were lower than R-114.
This efficient, trouble-free, quiet unit faded from the market because it could not compete aesthetically with the more modern, bottom-mounted refrigerators.
First prize must go to the original Monitor Top, the first successful sealed unit. The only parts that were not original were the refrigerant (sulfur dioxide) and the high-side float. (Homeowners loved the circular tube condenser as a means of drying a wet towel.)
The largest model was a side-by-side double-door unit with an evaporator in each section. The evaporators were porcelain, filled with a brine solution, and each had room for two ice trays. A high-side float fed both evaporators.
The model was huge, requiring four men to lift and lower it onto the cabinet. Its normal cycle time was a 1:2 ratio, 1 hr run and 2 hrs off.
The compressor was, without a doubt, an inventor’s nightmare. It had two attached pistons, one for oil about ¼ -in. dia, and the other about ¼ -in. for the vapor. There wasn’t any connecting rod and only one valve, a discharge valve. The double pistons were attached to a bearing that fitted over the throw of the crankshaft. As the crankshaft rotated, the piston body housing oscillated to follow the in-and-out movement of the pistons.
Two highly polished plates also oscillated, lining up two holes as the piston moved down and closed on the up movement. One hole came from the evaporator, and the other went to a slot in the piston body that was exposed when the piston reached bottom dead center. The oscillating plates were the suction valve for both the gas and lubricating oil.
If you laid out all the compressor parts on a table and closely examined each piece for its precise fit and finish, plus the pressure lubrication system, there would be no doubt in your mind that “This compressor will run forever.” Years later, compressors that were designed without a connecting rod were called “Scotch Yoke” compressors.
Even the relay was one of a kind. It had two coils separated by a V-shaped metal armature that could be attracted by either coil. One coil was in series with the run winding, and the other in parallel with the start winding.
It was actually a combination of a current and potential relay. The current coil was the first to be energized by the high amperage, and when the motor was almost up to speed and the amps reduced, the potential coil took over, attracting the armature, which opened the starting contact points.
The repair record was excellent. The first call was usually for a sulfur dioxide leak at the brazed connection from the high-side float into the porcelain evaporator that rusted and became porous (after running about 10 years). The improved model had a stainless steel evaporator. Many of the improved Monitor Top models were in use for more than 30 years, and were finally replaced because homeowners got tired of looking at them.
Servicing Sealed UnitsMost refrigerator manufacturers were starting to convert to the sealed unit just as WWII started. But it wasn’t until after the war ended, when the early sealed units were going out of their warranty periods, that service contractors started to repair them — and ran into a stone wall.
The only replacement parts available were relays and thermostats that were sold exclusively by authorized dealers, at very inflated prices. All manufacturers of sealed systems at that time claimed that no one was capable of repairing their units in the field. Therefore, every defective sealed unit had to be returned to the factory.
Because of this policy, all manufacturers refused to sell any of the units’ component parts, such as evaporators and compressors, to the independent service contractor. As a result of the program, every unit was designed to be removed from the box or fixture in one piece, to be shipped back to the factory in a custom-designed crate. This was indeed a very costly procedure.
With the advent of the two-door combination refrigerator-freezer, the return to the factory policy became impossible; all repairs had to be made in the field. So, manufacturers started selling compressors and evaporators.
Domestic RefrigerationIn the 1930s, there was a strict division between domestic and commercial repairs. It was unusual for a “commercial man” to be required to work on a domestic refrigerator, and vice-versa.
The home refrigerator was a diversified mess by comparison to commercial units. There were three kinds of refrigerant controls, low- and high-side floats and automatic expansion valves. There was an assortment of refrigerants: sulfur dioxide, methyl chloride, isobutane, methyl formate, R-114, Carrene, and R-12.
Refrigerator mechanics were required to know how to replace or tighten a belt without causing a shaft seal leak; replace refrigerant controls, motors, and compressors; and diagnose all the problems related to every kind of refrigerant.
Sulfur dioxide, in particular, presented an overwhelming problem if moisture entered the system after it was opened to the atmosphere. The combination of moisture and sulfur dioxide produced a gummy substance that attacked every moving part in the compressor. Stuck compressors were more frequent than today’s burnouts.
Discharging sulfur dioxide in any quantity was hazardous to anything living in the home or apartment — animal, human, or plant. Whenever possible, the gas was discharged into a pail filled with a solution of lye (potassium hydroxide) and water; this had a neutralizing effect on the toxicity and odor. Methyl chloride, aside from being flammable, would also yield a gummy substance when combined with moisture.
When R-12 was first used in hermetic units, a very peculiar service call would happen. The complaint would be, “After I defrost the refrigerator, it would start freezing and then it would stop freezing while it was running.” And sure enough, when the “Frigidaire man” ran the unit, the evaporator would start frosting, and after 10 minutes all the frost would disappear while the unit was still running. If he placed a hot, wet towel on the inlet tube of the evaporator, there would be a sudden inrush of refrigerant. Problem solved.
Moisture frozen at the cap tube outlet was causing all that trouble. But how was that possible when the system was never opened? Where did the moisture come from?
When the first hermetic units came on the scene, sulfur dioxide was the refrigerant and double cotton was the insulation used on the motor windings. If the winding should overheat, the first thing that was produced by the overheated cotton insulation was H2O — water. In a sulfur dioxide system, it was an instant disaster; but with R-12, the moisture from the overheated cotton insulation circulated until it froze at the cap tube outlet.
Ehrens is a refrigeration expert at Sealed Unit Parts Co. Inc., 2230 Landmark Place, Allenwood, NJ 08720; 732-223-6644.
Publication date: 04/30/2001